1. Technical Field
This invention relates to an apparatus for removing contaminants from a fluid, and in particular, for removing contaminants from a fluid while providing an indication when the apparatus is saturated with contaminants.
2. Background Art
Filters of various sorts have long been employed to filter contaminants from gasoline as the gasoline is being pumped from an underground reservoir at a service station into the tank of a vehicle. In many cases, the filter includes a filter medium including a mechanical filtering media to remove particulates from the gasoline and a water-absorbing material to remove water from the gasoline. An example of such a filter is disclosed in commonly assigned U.S. Pat. No. 4,623,560 issued to William R. Ayers on Nov. 18, 1986, the entire disclosure of which is herein incorporated by reference.
In use, the water-absorbing material within the filter begins to swell as water is absorbed. As increasing amounts of water are absorbed, the swelling becomes more pronounced, causing the pressure drop across the filter medium to increase. The swelling ultimately causes the flow of gasoline through the filter to decrease.
As the flow of gasoline through the filter is decreased, the delivery of gasoline to the vehicle tank is slowed. The slowing of delivery of the gasoline, in turn, means that a particular pump will be tied up for a longer period of time to deliver a given quantity of gasoline. As a consequence, fewer customers can be accommodated, and the income of the service station will suffer.
Even if a customer complains to the operator of the service station about a slower than normal filling process, the person in charge may do nothing more than check to see that gasoline is flowing through the filter, without checking the rate of flow. This is particularly likely to occur where relatively untrained personnel are in charge of a service station operation, such as is the case, for example, with the so-called "mini-marts".
Even when trained personnel are involved in the process and take the time to check the rate of flow through the filter, determining when a filter is sufficiently plugged (i.e. that the rate of flow is too low) as to require replacement requires a relatively subjective judgment. It would, therefore, be highly desirable to have a filter that provides a positive indication when filter replacement is required. The present invention is directed to meeting that need.